U.S. patent number 3,643,806 [Application Number 04/809,522] was granted by the patent office on 1972-02-22 for adjustable knife blade for dry filter cake discharge.
This patent grant is currently assigned to United States Filter Corporation. Invention is credited to Theodore H. O'Cheskey.
United States Patent |
3,643,806 |
O'Cheskey |
February 22, 1972 |
ADJUSTABLE KNIFE BLADE FOR DRY FILTER CAKE DISCHARGE
Abstract
An elongated knife blade spans the surface of a filter leaf,
with its inner end making a loose fit around the central shaft of
the filter. After the filtration process, the blade is held
stationary and the filter leaf is rotated under it to remove the
filter cake which has accumulated on the leaf. The spacing between
the blade and the surface of the leaf is adjustable so that the
cake left on the leaf can be set to the desired thickness. The leaf
can be rotated relative to the blade during filtration to
continuously remove cake from the leaf and thereby increase the
concentration of solids in the liquid circulated through the
filter.
Inventors: |
O'Cheskey; Theodore H.
(Whittier, CA) |
Assignee: |
United States Filter
Corporation (Whittier, CA)
|
Family
ID: |
25201525 |
Appl.
No.: |
04/809,522 |
Filed: |
March 24, 1969 |
Current U.S.
Class: |
210/327; 210/332;
210/396 |
Current CPC
Class: |
B01D
29/70 (20130101); B01D 29/41 (20130101); B01D
33/21 (20130101); B01D 29/6476 (20130101); B01D
33/466 (20130101) |
Current International
Class: |
B01D
33/21 (20060101); B01D 33/15 (20060101); B01D
29/41 (20060101); B01D 29/39 (20060101); B01d
029/34 () |
Field of
Search: |
;210/67,327,331,332,396 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Zaharna; Samih N.
Claims
I claim:
1. A liquid-filtering apparatus comprising a shell; a filter leaf
disposed within the shell; means for forcing liquid into the leaf
to form a cake on the leaf; an elongated knife blade disposed
adjacent the face of the filter leaf and extending outwardly from
the central portion of the leaf to its periphery, the knife blade
including an elongated support bar and a replaceable elongated
blade member having a longitudinal channel-shaped edge opposite its
blade edge for making a sliding fit over the support bar so that
the blade member may be removed when worn, the blade member being
constructed of polytetrafluoroethylene; means for adjusting the
space between the blade member and the surface of the leaf; rollers
adapted to ride on the perimeter of the filter leaf for supporting
the outer end of the knife blade; stop means secured to the
interior of the shell, the knife blade being secured to the stop
means; and means for rotating the leaf relative to the knife blade
so that the desired amount of cake is cut off the leaf by the blade
as the leaf rotates under it.
2. A liquid-filtering apparatus comprising a shell; a plurality of
filter leaves in the shell; means for forcing liquid into the
leaves to form a cake on the face of each leaf; a separate
elongated knife blade disposed adjacent the face of each filter
leaf, each knife blade extending outwardly from the central portion
of its respective leaf to the periphery of the leaf; means for
simultaneously rotating the knife blades and filter leaves relative
to the shell; and stop means on the interior of the shell for
engaging the moving knife blades in succession at different
angularly spaced locations around the interior of the shell to
successively prevent the blades from rotating relative to their
respective leaves so that filter cake is cut off each leaf by a
respective blade at a different location with respect to an
adjacent leaf.
3. Apparatus according to claim 2 including means for adjusting the
space between each knife blade and the face of its respective
filter leaf, the adjusting means including an elongated carrying
bar extending outwardly from the central portion of the leaf to its
periphery for supporting the knife blade, a plurality of
spaced-apart slotted holes extending lengthwise along the blade,
matching holes disposed in the surface of the carrying bar adjacent
the slotted holes, and fasteners extending through the slotted
holes into the holes of the carrying bar to secure the blade to the
surface of the carrying bar such that the blade is slidable
relative to the surface of the carrying bar toward or away from the
face of the leaf.
4. Apparatus according to claim 2 wherein each knife blade
comprises an elongated support bar and a replaceable elongated
blade member adapted to make a sliding fit over the support bar so
the blade member may be removed when worn.
5. Apparatus according to claim 4 wherein each blade member is
constructed of plastic material.
6. Apparatus according to claim 2 wherein each knife blade has a
hardness less than that of the filter leaf so that the entire
filter cake can be removed from the leaf while substantially
preventing wear on the filter leaf.
7. Apparatus according to claim 2 wherein each knife blade is
supported at its outer end by a separate roller which rides on the
periphery of the filter leaf.
8. A liquid-filtering apparatus comprising a shell; a plurality of
filter leaves disposed within the shell; means for forcing liquid
into the leaves to form a cake on the face of each leaf; a separate
elongated knife blade disposed adjacent the face of each filter
leaf, each knife blade extending outwardly from the central portion
of its respective leaf to the periphery of the leaf; angularly
spaced-apart stop means secured to the interior of the shell, each
stop means being secured to the shell at a point adjacent a
respective one of the filter leaves, with each stop means extending
inwardly toward the filter leaves a distance which is different
from that of the stop means corresponding to the other filter
leaves; a separate stop-engaging means extending outwardly from
each knife blade toward a respective one of the stop means, each
stop-engaging means extending outwardly a distance which is
different from that of the stop-engaging means corresponding to the
other knife blades; and means for producing relative rotation of
the knife blades and their respective filter leaves so that each
stop-engaging means comes in contact with its respective stop means
to prevent the blades from rotating with their respective leaves so
that filter cake is cut off each leaf by the blade, whereby the
stop-engaging means engage the stop means at a plurality of
locations about the periphery of the leaves so that cake is cut off
each leaf surface at a different location with reference to the
adjacent leaves.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improvement in rotary pressure leaf
filters, and more particularly to an apparatus for removing the
cake which accumulates on the outer surfaces of filter leaves
during the filtration process.
A conventional pressure leaf filter comprises a plurality of filter
leaves mounted on a hollow, rotatable shaft in a cylindrical tank
or shell. Liquid to be filtered is introduced into the shell under
pressure and forced through the leaves which deliver the filtrate
to the hollow shaft for collection. During the filtering process,
solids suspended in the liquid accumulate on the surface of the
leaves as a cake, and eventually interfere with filtering
efficiency. If the filter cake buildup on a leaf is substantial,
the pressure drop through the leaf is sufficient to cause the leaf
to collapse. Therefore, the filter cake is removed periodically to
maintain efficient operation and prevent destructive loading.
Filter cake is usually removed or "sluiced" from the leaves by
emptying the filter shell and directing a spray of cleaning liquid
under pressure onto the leaf surfaces. However, there are instances
where it is desirable to remove filter cake from the leaves in a
dry or semidry condition, instead of sluicing it from the leaves.
For example, dry filter cake is often a valuable byproduct of the
filtration process; consequently, it is desirable to recover the
cake intact at the end of a filtering cycle. Furthermore, dry cake
discharge is necessary in some applications where the filter cake
is incapable of being sluiced from the leaves because of the
particular nature of the produce involved.
Removal of dry cake at the end of each cycle also permits reuse of
the same precoat materials for succeeding filtration cycles. For
example, filter leaves are usually "precoated" before each cycle
with a filtering media which enhances the filtering capabilities of
the leaves. During the filtering process, the solids removed from
the liquid to be filtered collect on the surface of the precoat
layer. At the end of a cycle, all accumulated filter cake is
removed down to and slightly into the precoat layer. Then, after
the filter cake is removed from the filter shell, the remaining
precoat layer is removed from the leaves, reslurried, and reapplied
to leaf surfaces for reuse as the precoat layer for the next
filtration cycle. This process represents a significant savings of
filtration time and cost of precoat materials.
Past methods for removing dry cake from filter leaves have not
proved satisfactory. This is particularly true where accurate
control of cake removal is desired. In some prior available
pressure leaf filters, the leaves are removed from the filter shell
and replaced during cleaning. This procedure is cumbersome and
time-consuming because the entire filtering assembly must be
dismantled. Moreover, it does not permit use of the same precoat
materials for succeeding filtration cycles. In other pressure leaf
filters, dry cake is vibrated from the leaves by an agitator or
blown off the leaves with compressed air. These methods likewise
prevent accurate control of filter cake removal.
SUMMARY OF THE INVENTION
The apparatus of this invention includes a knife blade disposed
adjacent the surface of a filter leaf in the shell of conventional
liquid filtration apparatus. Liquid to be filtered is introduced
into the shell and forced through the leaf to form a cake on the
surface of the leaf. The knife blade extends outwardly from the
central portion of the leaf to its periphery and becomes embedded
in the filter cake during the filtration process. Means are
provided for effecting relative rotation of the blade and the leaf
so that the cake is cut off the leaf by the blade. The space
between the blade and leaf is adjustable so that the desired amount
of cake is removed. Thus, filter cake is rapidly removed from the
leaves for recovery or disposal by a device which is simple in
construction and easily operable while requiring a minimum of
cleaning time.
In the preferred form of the invention, the filter leaf is mounted
on an elongated rotatable shaft disposed axially within the shell.
The inner end of the knife blade makes a loose fit around the
shaft, and the outer end of the blade is preferably supported by
rollers which ride on the perimeter of the filter leaf. The filter
leaf is keyed to the center shaft and rotates with it during
cleaning. The rollers firmly support the end of the knife blade to
insure uniform filter cake cutoff. Stop means are secured to the
interior of the shell, and during cleaning operations the leaf is
rotated with the blade embedded in the cake until the end of the
blade strikes the stop means. This prevents the blade from rotating
with the leaf so that the filter cake is cut off the leaf as the
leaf rotates under the blade.
When the apparatus of this invention is used in filters having a
plurality of spaced-apart filter leaves, stop means are secured to
the interior of the shell adjacent the periphery of each leaf.
Preferably, the stop means of adjacent leaves are angularly
displaced from one another so that the filter cake is cut off each
leaf at a different location relative to the adjacent leaves. This
avoids overloading the motor which rotates the shaft during
cleaning, because the loads to which the motor is subjected by each
blade engaging its respective stop are spaced instead of applied
simultaneously. Since the filter cake is cut off adjacent leaves at
different locations, the removed filter cake does not ball up or
"bridge" across adjacent leaves and prevent proper cake discharge
from the shell.
This invention contemplates a method of filter cake removal which
enables filtration apparatus to be used to increase the
concentration of solids suspended in a particular liquid. A filter
leaf is mounted in the shell of liquid filtration apparatus and an
elongated knife blade is disposed adjacent the face of the leaf.
The liquid containing the solids is forced into the shell and
through the leaf so that a cake of solids is formed on the leaf.
Relative rotation of the leaf and blade is produced as the cake is
formed so that the solids are continuously cut off the leaf by the
blade and reslurried in the liquid within the shell. As a result,
the filter acts as a thickener because a heavy concentration of
solids builds up in the liquid inside the shell.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view, partially broken away, showing a
conventional filtration shell and the apparatus of this
invention;
FIG. 2 is a fragmentary plan elevational view of the apparatus of
this invention;
FIG. 3 is a fragmentary sectional elevational view, partially
broken away, taken on line 3--3 of FIG. 2;
FIG. 4 is a sectional elevational view taken on line 4--4 of FIG.
2;
FIG. 5 is an elevational view showing an alternate embodiment of
the stop means of this invention; and
FIG. 6 is a sectional elevational view showing an alternate
embodiment of the knife blade of this invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to the drawings, a substantially circular filter leaf 10
is secured to the hub 12 of an elongated, hollow rotatable shaft
14. The shaft and filter leaf are centrally disposed within a
cylindrical filtration tank or shell 16. During operation of the
filtration apparatus, liquid to be filtered is introduced into the
shell and forced under pressure against each side of filter leaf
10, as indicated by the arrows in FIG. 3. The liquid then passes
down through a filtering cloth 17 covering the outer surface of the
leaf and flows radially inwardly through the interior of the leaf
and into the interior of shaft 14 for collection.
An elongated knife blade 18 is secured by bolts 20 to a flat,
elongated carrying bar 22 welded at its inner end to a sleeve 23
which makes a loose fit around hub 12. The bolts pass through a
series of spaced-apart slotted holes 24 in the blade, and are
screwed into threaded holes 24a in the carrying bar. The slotted
holes enable the blade to be moved toward or away from the leaf
surface to set the desired thickness of cake remaining on the leaf.
Typically, the blade is set to be spaced about one-sixteenth inch
from the leaf.
A pair of laterally spaced shafts 25 are welded to the end of the
carrying bar and project outwardly past the outer rims 26 of the
filter leaf. A separate roller 28 is mounted on each of the shafts
25 to ride on the outer rim of the leaf. A flat, L-shaped bracket
30 having an outwardly projecting arm 30a is secured to the ends of
the shafts by washers 32 and hex nuts 33. The bracket spans the
periphery of the filter leaf and is similarly secured to another
carrying bar and knife blade of identical construction mounted on
the opposite face of the filter leaf.
During filtration process, the filter leaf is held stationary and
the knife blade hangs free as the filter cake builds up around it
on the leaf. The hub is keyed on the shaft so that the hub and the
leaf rotate with the shaft. After a filter cake of prescribed
thickness is built up, cleaning operations are initiated by
emptying the shell and blowing air through the cake to dry it out.
The cake is then removed from the leaf by rotating the shaft, and
therefore the leaf, in the direction indicated by the arrows in
FIGS. 1 and 2. The leaf rotates with the blade embedded in the cake
until bracket 30 strikes a stop 34 welded to the interior surface
of the shell. The stop is an elongated bar disposed longitudinally
along the inner surface of the shell on legs 35 so that it projects
outwardly from the surface a distance sufficient to engage the
bracket. When the blade engages the stop, it remains stationary
while the leaf rotates under it to cut off the filter cake which
falls into a trough (not shown) located at the bottom of the
shell.
In a multileaf filter, each filter leaf carries its respective pair
of knife blades. Preferably, a second elongated stop 36 is
longitudinally disposed within the shell adjacent stop 34, and
extends further into the shell than stop 34. The arms 30a of
alternate brackets 30 are slightly longer than the arms of the
remaining brackets so that the shorter arms clear stop 34 and
strike stop 36, while the longer arms strike stop 34. In use, the
knife blades of alternate leaves engage alternate stops, as shown
in FIG. 1. This prevents the sudden overloading of the motor (not
shown) which rotates the shaft during cleaning.
FIG. 5 shows an alternate embodiment of the invention wherein the
knife blade is adapted to be held in a stationary position adjacent
the face of the leaf during the entire filtration process. An
elongated bar 38 extending the length of the shell is welded to the
inner wall of the shell and projects outwardly from the wall a
distance sufficient to engage arms 30a of bracket 30. The arm of
the bracket is permanently affixed to the bar by bolts 40 which
extend through a series of spaced-apart slotted holes 42 in arm
30a, and are screwed into cooperating threaded holes (not shown) in
the bar. The slotted holes enable the blade assembly to move back
and forth slightly in the radial direction as the leaf rotates.
This loose fit compensates for any eccentricity in the leaf, and
for any rotational imbalance in the rotary shaft. This particular
embodiment of the invention enables the filter to be used as a
liquid-thickening device. That is, a stock of liquid containing
thinly distributed solids can be circulated through the filter
under pressure to produce an end product having a thick
concentration of solid material. The blade is held stationary
adjacent the face of the leaf and the leaf is rotated continuously
during filtration. A cake of solids builds up on the leaf as the
stock of liquid is forced into the shell and through the leaf, and
the solids are constantly shoved off the leaf by the blade as the
leaf rotates. The removed cake is reslurried in the liquid within
the shell, and as the stock of liquid and solids is constantly fed
into the shell, the concentration of solids in the shell
continuously increases to eventually produce a liquid having a
substantial concentration of solids.
The knife blade of this invention is preferably constructed of a
strong, corrosion-resistant metal such as stainless steel. However,
in some applications it is desirable to construct the blade out of
a tough, durable plastic material such as Teflon. This allows
adjustment of the blade to remove the complete cake, including any
precoat material, without causing undue wear on the filtering cloth
17. FIG. 6 shows an alternate embodiment of the invention wherein
the knife blade has a removable plastic edge which can be replaced
when worn. An elongated support bar 44 is secured by bolts 20 to
carrying bar 22. The bolts pass through a series of spaced-apart
slotted holes in the support bar to facilitate moving the bar
toward or away from the leaf surface. A replaceable elongated
plastic blade member 46 makes a sliding fit over the edge of the
support bar adjacent the leaf. The blade member has a longitudinal
channel-shaped edge 48 which fits over the support bar, and an
opposed longitudinal blade edge 50 for cutting filter cake off the
leaf.
* * * * *